J. H. C. Hoge

Bio: J. H. C. Hoge is an academic researcher from Leiden University. The author has contributed to research in topics: Gene & Gene expression. The author has an hindex of 22, co-authored 34 publications receiving 1641 citations.

Coordinated regulation of two indole alkaloid biosynthetic genes from Catharanthus roseus by auxin and elicitors.

Abstract: Catharanthus roseus (periwinkle) produces a wide range of terpenoid indole alkaloids, including several pharmaceutically important compounds, from the intermediate strictosidine. The complete mRNA sequence for the enzyme strictosidine synthase (SSS) was determined. Comparison of the primary structure of the encoded protein with the amino-terminal sequence of purified SSS indicated the presence of a signal peptide of 31 amino acids in the putative primary translation product. SSS is encoded by a single-copy gene indicating that isoenzymes reported by others are formed post-translationally from a single precursor. The sss gene and the tryptophan decarboxylase gene (tdc), encoding another enzyme essential for indole alkaloid biosynthesis, are coordinately regulated. In plants steady-state mRNA levels are highest in roots. In cell suspension cultures the genes are rapidly down-regulated by auxin. In contrast, both genes are strongly induced by fungal elicitors such as Pythium aphanidermatum culture filtrate or yeast extract. Induction is a rapid, transcriptional event occurring independent of de novo protein synthesis. These results show that a first important regulatory step in the complex process leading to indole alkaloid accumulation in C. roseus suspension cells is transcription of the biosynthetic genes.

Tobacco genes encoding acidic and basic isoforms of pathogenesis-related proteins display different expression patterns

Abstract: The induction by cytokinin stress and ethylene of nine different tobacco mosaic virus-inducible mRNA classes (termed A-I) encoding pathogenesis-related (PR) proteins was studied. The induced mRNA levels were compared to basal levels in healthy tobacco plants grown in tissue culture and in a greenhouse. Cytokinin stress and ethylene were found to induce different subsets of the mRNAs, indicating that ethylene is not the primary inducing signal in cytokinin-stressed shoots. mRNAs F, H and G encoding the basic hydrolytic enzymes chitinase, β-1,3-glucanase and a basic equivalent of PR-1, respectively, were found to be expressed at high levels in roots of healthy plants. mRNAs D, I and B encoding the acidic equivalents of the proteins proved to be present at low levels in healthy plants. These results indicate that genes encoding basic and acidic isoforms of pathogenesis-related proteins are differentially regulated.

Promoters of auxin-induced genes from tobacco can lead to auxin-inducible and root tip-specific expression.

Abstract: In previous studies we have identified several mRNAs which accumulate after addition of 2,4-dichlorophenoxyacetic-acid (2,4-D) to auxin-starved tobacco cells. The mRNAs corresponding to cDNA clone pCNT103 were found to accumulate transiently prior to the cell division response due to auxin treatment. In this study we determined the sequences of three 103-like cDNAs and two 103-like genes, GNT1 and GNT35. To further study the regulation of the expression of these genes their 5' regions were translationally fused with the beta-D-glucuronidase reporter gene (GUS). The GNT1 5' region led to GUS expression only in the root tips of transgenic plants. By using transgenic hairy-root cultures and transformed cell suspension cultures it was shown that the 5' regions of both GNT1 and GNT35 lead to 2,4-D-inducible expression of GUS activity. The homology of the 103-like genes with other auxin-regulated genes is evaluated.

Plant cell biotechnology for the production of alkaloids: present status and prospects'

Abstract: hsmcr.-The culture ofplant cells on a large scale in bioreactors has been shown to be feasible. The price of a plant cell biotechnological product is mainly governed by the slow growth of plant cell cultures, making the depreciation costs of the bioreactor the major costdetermining factor. A review of the production of the economically important alkaloids in plant cell cultures shows that presently only berberine and sanguinarine are being produced. Important factors to be considered in connection with accumulation of alkaloids are biosynthetic rate, accumulation site, and catabolism. Recent studies in the field of the regulation of the biosynthesis of terpenoid indole alkaloids on the level of genes and enzymes are reviewed, showing that it is feasible to clone genes from secondary metabolism and express these in various other plants. Concerning storage, it seems that compartmentation also plays a role in the regulation of alkaloid biosynthesis. Furthermore, catabolism of terpenoid indole alkaloids in cell cultures is an important factor, at some point even equalling the rate of de novo biosynthesis. The ongoing studies on regulation of alkaloid biosynthesis might eventually lead to transgenic plants or plant cell cultures with an improved productivity of the desired compounds. This knowledge is also of interest in connection with studies on the role of secondary metabolism for plants, and may contribute to a better understanding of resistance of plants to diseases and various herbivores. Of all known natural products, about 20% (i.e., about 16,000) are classified as alkaloids. For many of these alkaloids biological activities have been reported, but presently only about 30 are commercialized (1). Most of these are medicines, but some are used as flavoring, poison, and model compounds for pharmacological studies. These alkaloids can be qualified as specialty chemicals, as their worldwide production volume is limited; alkaloids such as quinine and quinidine have a yearly production of 300-500 metric tons, ajmalicine about 3600 kg, and compounds like vinblastine and vincristine in the kilogram range only (2,3). The amounts of plant material needed for the extraction of these compounds are, compared to agricultural crops, very small. For the examples mentioned this is in the order of 5000-10,000 metric tons ofCinchonu bark for the extraction of quinine and quinidine and 200-300 tons of Catharanthus roseus roots for the production of ajmalicine. The value ofeach of the markets of the major alkaloids can be estimated to be in the range of several hundred million dollars (4). These specialty chemicals are now produced by extraction from plant material that is cultivated or sometimes even still collected in the wild. There are several problems connected with this production method. Variable quantities and qualities of the plant material, plants that need to grow several years before they are ready for harvesting (e.g., Cinchona bark), and over-collecting of endangered species (e.g., Taxus hev$olia)

Clonal analysis of heterogeneous crown gall tumor tissues induced by wild-type and shooter mutant strains ofAgrobacterium tumefaciens-expression of T-DNA genes.

Abstract: Tumors were induced by anAgrobacterium tumefaciens strain with a wild-type octopine Ti plasmid and by shooter mutants with a transposon insertion in the auxin-locus of the T-region. Cloning of isolated axenic tumor tissues revealed that in all cases they consisted of tumor cells (10–26%) next to a majority of normal cells. The tumor clones that had been induced by the strain with the wild-type Ti plasmid all grew as amorphous calli. Tumor, clones induced by a shooter mutant were of two different types. One type of clone grew well on phytohormone-free medium. this type invariably regenerated tumorous shoots abundantly on this medium. The other type of clone only grew after the addition of auxin and cytokinin to the culture medium, but slow growth also took place in the presence of only auxin. This type never regenerated shoots spontaneously. After stimulation by a high level of kinetin, however, a few shoots were also obtained from these clones. One of these shoots, like other tumorous shoots, contained the tumor-specific enzyme octopinesynthase (Ocs), but in contrast to other tumorous shoots formed a root-system. The expression of T-DNA genes in shoots proliferating from the cloned tumor tissues induced by a mutant with an insertion in the region for transcript tr. 2 was studied by northern blot hybridization. Except for tr.2 the T-DNA transcripts were detected in the tumorous shoots analysed, including the transcript, tr.1 from the auxin-locus and tr.4 from the cytokinin-locus. This shows that the presence of these transcripts, which are assumed to be responsible for the tumorigenic character of tumor cells, does not interfere with the differentiation of shoot cells. One of the shooty tumor clones (TSO38) showed an unstable character with regard to octopine synthase activity (Ocs±). For, TSO38 and some of its subclones, it was found that only 4% of the regenerated shoots were Ocs+. Northern blot hybridization revealed that the mRNA for octopine synthase was present in extremely low quantity in the population of TSO38 derived shoots. The finding that it was possible to force shoots from clone TSO38 and from subclone TSO38-23− that were Ocs− to become Ocs+, proved that the gene for octopine synthase was present in the Ocs− shoots and that this gene showed unstable expression due to regulation at the level of transcription.

Stress-Induced Phenylpropanoid Metabolism.

Abstract: Phenylpropanoid compounds encompass a wide range of structural classes and biological functions. Limiting discussion to stress-induced phenylpropanoids eliminates few of the structural classes, because many compounds thst are constitutive in one plant species or tissue can be induced by various stresses in another species or in another tissue of the same plant (Beggs et al., 1987; Christie et al., 1994).

The functions and regulation of glutathione s-transferases in plants.

Abstract: ▪ Abstract Glutathione S-transferases (GSTs) play roles in both normal cellular metabolism as well as in the detoxification of a wide variety of xenobiotic compounds, and they have been intensively studied with regard to herbicide detoxification in plants. A newly discovered plant GST subclass has been implicated in numerous stress responses, including those arising from pathogen attack, oxidative stress, and heavy-metal toxicity. In addition, plant GSTs play a role in the cellular response to auxins and during the normal metabolism of plant secondary products like anthocyanins and cinnamic acid. This review presents the current knowledge about the functions of GSTs in regard to both herbicides and endogenous substrates. The catalytic mechanism of GST activity as well as the fate of glutathione S-conjugates are reviewed. Finally, a summary of what is known about the gene structure and regulation of plant GSTs is presented.